Due to various kinds of leverage in the economic system, a 5% drop in demand would probably get multiplied into a 20% drop in GDP and a total wipeout of the financial system along with a wipeout of the political system too.
The other way to do it is to have a mass withdrawal of cash from the banking system and/or the brokerage firms.
The sad part of the USA today is that due to leverage, a minor blip could crash the system, whereas in the old days, even a US Civil War could not.
There really is too big to fail and the fed implements QE to infinity because even a 1% drop in GDP could crash the system.